The subject invention is directed to the art of measuring systems and, more particularly, to method and apparatus for electrically and mechanically connecting measuring systems such as general gauge-type devices to operatively associated support members.
In this application, xe2x80x9cmeasuring systemxe2x80x9d refers to an electrostatic or electrodynamic meter movement, i.e. a moving coil instrument or moving iron instrument with a corresponding element inside, namely, a measuring coil. Meter movements of this kind are used in automotive engineering, for example, in order to display parameters such as acceleration, speed, fuel gauge readings, and the like on an automotive control panel. As is known, a meter movement displays the flow of current as the electric variable by means of an inductive reaction between coils in the measuring device resulting in a rotary movement of an output member acting against a spring force. For the desired functions such as speedometer or fuel gauge application, the known actual values are transformed into current values with the aid of electronic circuits so that they can be displayed with the aid of a meter movement.
Measuring systems of the type under consideration are often joined to support members or plates in a number of different ways. Typically, mounting is accomplished by means of screws or the like. One drawback to this method, however, is that substantial time and effort is required for tightening the screws to adequately connect the measuring system to the support plate. In addition, in order to establish suitable electrical connections to the measuring system, soldering steps or the like are also often required in order to ensure the necessary electrical integrity between the measuring system and the support member. Generally, fastening and soldering are time consuming and awkward.
Accordingly, in DE-A-195 19 834, a connection between a measuring system and a support member is proposed wherein the measuring system can be connected quickly with the support by means of a bayonet catch mechanism. As described in the ""834 patent, electric contact between the measuring system and the support member is effected using elastic tongues arranged at the outer surface of the measuring system. The tongues are pressed by a spring force against designated contact areas on the support member when the measuring system is fastened to the support member.
With the above type arrangement between the measuring system and the support member, unwelcome twisting may occur after the connection is established as a result of external mechanical influences such as, for example vibration. When this happens, the contact tongues and the electric areas often become disengaged. In addition, complete detachment of the bayonet catch from the support member may also occur. Moreover, with the type of connection described, mechanical influences may also adversely affect the integrity of the one or more electrical connections between the measuring system and the support member. Since the electrical contacts are held in place by spring force alone, deterioration of the electrical contact connection may also occur.
The subject invention provides a measuring system and a method and apparatus for electrically and mechanically connecting the measuring system to an operatively associated support member that overcomes the noted problems and results in a cost effective measuring system which enables simple, cost effective, and robust connection with a support plate as well as an arrangement of such measuring system on the support plate which prevents accidental twisting and/or separation of the measuring system from the support plate after installation.
In particular, and in accordance with one aspect of the invention, there is provided a measuring system including a substantially cylindrical housing defining a bottom surface and a lid surface. A plurality of spaced apart elastic locking tongues are carried on an outer circumference of the cylindrical housing. The locking tongues are adapted to be received and lock into a corresponding plurality of suitably arranged cavities defined in an associated support plate when the measuring system is selectively brought into aligned engagement with the associated support plate.
In accordance with a more limited aspect of the invention, the measuring system includes a plurality of spaced apart electric contact pins extending from the bottom surface of the cylindrical housing. The contact pins are adapted for insertion into a corresponding plurality of suitably arranged contact cavities defined in the associated support plate.
Preferably, the plurality of spaced apart contact pins have a quadratic cross-section. In addition, the plurality of spaced apart contact pins include contact areas defining flexible press-in zones with first profiles for engagement with complimentary shaped second profiles formed by the plurality of contact cavities. The contact pins are preferably adapted for gas-tight contact with the corresponding plurality of contact cavities. Further, the contact pins are preferably tin plated.
In accordance with a still further limited aspect of the invention, the measuring system includes at least one centering member extending from the bottom surface of the cylindrical housing. The centering member is adapted for insertion into a corresponding at least one suitably arranged centering cavity defined in the associated support plate.
Preferably, the centering members extend from the bottom surface of the cylindrical housing by a first predetermined distance which is greater than a second predetermined distance that the plurality of elastic locking tongues extend from the bottom surface of the housing. In that way, the centering members engage the face surface and/or centering cavities of the associated support member before the elastic locking tongues when the measuring system and support member are brought together toward their final assembled condition. The engagement between the centering members on the housing with the centering cavities provided on the support member ensure proper alignment between the measuring system and the support member and prevent relative rotation therebetween.
Lastly, preferably, the elastic locking tongues extend from the bottom surface of the housing by a distance greater than the distance that the contact pins extend from the cylindrical housing. In that way, the contact pins engage the corresponding plurality of contact cavities in the support plate after both the centering members and the plurality of locking tongues establish mechanical contact with the associated support plate.
As can be seen from the foregoing, the primary object of the invention is the provision of a measuring system that includes elastic tongues arranged in a spaced apart relationship on the outer circumference of a cylindrical housing body, the elastic tongues being adapted to engage corresponding cavities formed in an associated support plate so that a secure mechanical connection is established thereby preventing subsequent unwelcomed inadvertent or accidental twisting and/or separation between the measuring system and the support plate. In the preferred arrangement, the plurality of locking tongues are formed integrally on the housing such as, for example, by injection molding. This arrangement provides for a cost effective manufacture of the subject measuring system and its housing while enabling a subsequent rapid and simple installation of the measuring system onto the support member.
Preferably, the support plate includes electrical conductors and, therefore, is formed as a conductor plate. For establishing electrical contact with the conductors in the support plate, a plurality of contact pins are provided and protrude from the underside of the measuring system. The contact pins are selectively inserted into a corresponding plurality of contact cavities formed in the support plate. With the connection described above, simultaneous electrical and mechanical connection between the measuring system and the support plate is simultaneously established.
The electrical connection between the contact pins and the plurality of contact cavities during connection of the measuring system with the support plate is effective, for example, by mechanical interference pressing and/or subsequent soldering.
In the preferred embodiment of the invention, the plurality of contact pins have a quadratic cross-section. The corresponding plurality of contact cavities are preferably formed with a substantially round cross section. This permits the use of cost effective commercial contact pins and conductor plates. In the preferred embodiment described, a line contact is established between the outer surfaces of the plurality of contact pins and the inner wall surfaces of the circular contact cavities. The line contact zones are formed alongside the edges of the contact pins. In such arrangement the connection pins of the measuring coil itself beneficially serve as contact pins. Other profiles of the contact pins and/or contact cavities are also contemplated including forming square contact cavities and cylindrical contact pins as well as other complementary forms and arrangements.
Preferably, the contact pins have free ends with a tapered shape and/or the apertures of the contact cavities are formed in a funnel shape in order to help facilitate the operative connection between the measuring system and the support member. The tapered shape of the contact pins and/or the funnel shape of the contact cavities provide a self-centering effect during relative motion between the contact pins and the contact cavities as the measuring system and support member are brought together toward their final assembled condition.
In a further embodiment of the invention, the contact cavities are formed as perforations extending through the support member. In that embodiment, the contact cavities formed as perforations accommodate the contact pins passed therethrough and establish an electrical contact therewith along the sides of the contact pins. This permits, in a beneficial fashion, a gas-tight connection between the contact locations or the contact areas of the contact pins and the contact cavities. The above constructions further contribute to an improvement in the electrical connection between the contact pins and the respective contact cavities.
In another embodiment, the electrical connection enables plating of the contact cavities with a tin alloy and/or a tin plating of the contact pins. Further, it is also contemplated that the contact cavities and/or contact pins are coated with another alloy or substance having good electrical conductivity properties such as, for example, gold plating.
In order to prevent unwelcome mechanical stresses at the contact pins during installation, at least one centering bolt is provided on the measuring system. The at least one centering bolt is introduced into a corresponding suitably arranged at least one centering cavity formed in the support plate when the measuring system and support plate are brought together. In order to facilitate insertion into the centering cavity, the centering bolts are preferably formed with a tapered free end. Likewise, the corresponding centering one or more cavities provided on the support member are selectively provided with a funnel-shaped aperture for the above purpose.
Lastly, the present invention also contemplates constructions that are the respective kinematic reverse of those described herein.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.